Mixing oil weights

I have a Ford 300 inline in my '95 F150. It's in great shape; 105,000 well-maintained miles. It had a rattle for the 1st couple seconds on cold start. I remember a guy I worked with years ago bought one new that did it. The dealer "normalized" it. "They all do that". :rolleyes:

I put a switch on the primary coil wire to kill spark. I crank the engine for a few seconds to build some oil pressure, then throw the switch. -No more rattle.

I wouldn't use an oil mix of what you think is good for the engine.